RE: TSV-ART review of draft-ietf-core-coap-tcp-tls-07

[Brian Raymor <[e-mail]>]

Thanks for your feedback.

> 1: It is not clear how the protocol reacts the errors from transport layers (e.g. connection failure).
>    The protocol will just inform apps of the events and the app will decide what to do or the protocol itself will do something?

The WebSockets case is addressed by RFC6455:

   When the underlying TCP connection is closed, it is said that _The
   WebSocket Connection is Closed_ and that the WebSocket connection is
   in the CLOSED state.  If the TCP connection was closed after the
   WebSocket closing handshake was completed, the WebSocket connection
   is said to have been closed _cleanly_.

-and-

   If at any point the underlying transport layer connection is
   unexpectedly lost, the client MUST _Fail the WebSocket Connection_.

It's possible to add language similar to the abort case, along the lines of "When the underlying TCP connection is closed or reset, the CoAP connection is closed and in flight messages may be lost".

> 2: There will be situations where the app layer is freezing while the 
> transport layer is still working. Since transport layers cannot detect 
> this type of failures, there should be some mechanisms for it somewhere in the protocol or in the app layer.  The doc needs to address
> this point. For example, what will happen when a PONG message is not returned for a certain amount of time?

PONG is modeled on similar mechanisms in RFC6455 and RFC7540. Neither provides any guidance for this case. It's expected that an application framework would define and enforce the appropriate policy for timeouts or retries.
 
> 3: Since this draft defines new SZX value, I think the doc needs to update RFC7959. This point should be clarified more in the doc.

Carsten responded to this issue and the final exchange is here - https://www.ietf.org/mail-archive/web/core/current/msg08562.html 

My sense is that we should treat this as an update to RFC7959 based on the original language:

     The value 7 for SZX (which would
      indicate a block size of 2048) is reserved, i.e., MUST NOT be sent
      and MUST lead to a 4.00 Bad Request response code upon reception
      in a request.

and the use of "extension" in coap-tcp-tls:

    The ’Block-wise Extension for Reliable Transport (BERT)’ extends the Block protocol
    to enable the use of larger messages over a reliable transport.

The existing IANA entries for Block1 and Block2 will also need to reference coap-tcp-tls in addition to RFC7959.

Tracking in https://github.com/core-wg/coap-tcp-tls/issues/129